Palladium, Platinum, Silver, and Gold

Distances indicate delocalization a over PCCO fragment of chelate ring 

Co-ordination geometry of NO2 h, h is determined by bulkiness of terdentate ligand and varies b, h 

Square-planar 20, 2N geometry, c H2N(CH2)3CHN fragments bridge the palladium atoms syn-syn structure with Pd d 

Trimeric units Pd—S(mean) 1328 A Near square-planar co-ordination Pd bonded to two carbene atoms with Pd—C 1.953 and 1.972 A Square-planar co-ordination 

Bridging by two azenido groups s See text 12 atom polyhedron is 6b a very distorted icosahedron 

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PART II Palladium, Platinum, Silver, and Gold by D. W. Clack... 

This volume is concerned with fundamental developments in the coordination chemistry of the elements of Groups 9-12 since 1982. The individual chapters cover the coordination chemistry of cobalt, iridium, nickel, palladium, platinum, copper, silver and gold, zinc and cadmium, and mercury. Unfortunately, because of factors beyond the Editors control, the manuscript for the proposed chapter on rhodium was not available in time for publication. 

For example, the results in Table 3 suggest that binary carbonyls of copper, silver and gold which have been detected spectrometrically in matrices at very low temperatures27, contain metal-CO bonds which are approximately of the same strength as those in Mn2(CO)i0. Similar considerations apply to carbonyls of palladium and platinum which have also been detected by matrix isolation spectrometry28. All of these binary compounds are unstable with respect to [M(c) + CO(g)J at room temperature. 

A series of pubKcations was devoted to the electrocatalytic reduction of nitrate by the Eindhoven group [50-54]. On the basis of these works, a comparative study was performed to determine the reactivity of nitrate ions in 0.1 mol dm concentration on eight different polycrystaUine electrodes (platinum, palladium, rhodium, ruthenium, iridium, copper, silver, and gold) in acidic solution using cyclic voltammetry, chronoamperometry, and differential electrochemical mass spectroscopy (DEMS) [50]. 

The relations expressed by equations (VII-21) and (VII-22) are valid for overvoltage at mercury, silver, palladium, aluminium, copper and gold at current densities ranging from 10 to 10-1 A/sq. cm. Other metals show different behavior. So, for instance, for graphite and lead values of 6 up to 0.3 have been measured whilst for platinized platinum the unusually low value of 6 = 0.025 has been found, which increases with time in case of smooth platinum the growth of the constant from the value 0.075 to 0.19 with time has been also observed. 

In alkaline solution the activity of the colloidal platinum increases to a maximum with increase of alkalinity, and then decreases. In this respect it behaves in an analogous manner to certain inorganic ferments.9 Exposure to Rontgen rays retards the reaction.10 Colloidal rhodium,11 palladium, iridium,12 silver, and gold behave in an analogous manner... 

Chromium, Molybdenum, and Tungsten Manganese and Rhenium Iron, Ruthenium, and Osmium Cobalt, Rhodium, and Iridium Nickel, Palladium, and Platinum Copper, Silver, and Gold Zinc, Cadmium, and Mercury Indium and Thallium Lead... 

The presence of zero-valence palladium and platinum in nanocomposites also has been examined by the absorption spectra. The wide bands of 200-330 nm due to these metal nanoparticles gradually drop down into the long-wavelength range (Fig. lb). These spectra, unlike silver and gold ones, demonstrate the lack of the individual bands for plasmons absorption that may be considered as a consequence of less degree of freedom of electrons in Pd and Pt [5]. 

It is pointed out forcibly that copper, silver, and gold form transition elements Ixd.woeu nickel, palladium, and platinum on the one hand and zinc, cadmium, and mercury on tin other hand. It is to be observed from Table VIII that enpi>er, silver, anil gold bike an intermediate position with rcsiiect to fusibility, volatility, coefficient of expansion, and atomic volumes. 

Ruthenium, osmium, rhodium, iridium, palladium and platinum are the six heaviest members of Group VII1. They are rare elements platinum itself is the commonest with an abundance of about 10-6% whereas the others have abundances of the order of 10"7 % of the earth s crust. They occur in Nature as metals, often as alloys such as osmiridium, and in arsenide, sulfide and other ores. The elements are usually associated not only with one another but also with the coinage metals copper, silver and gold. The main suppliers are South Africa, Canada and the USSR. 

Noble metals applied as electrocatalysts for the oxygen reduction have been largely utilized because of their high electrocatalytic activity and stability. Investigations are concentrated on platinum, palladium, silver and gold. The application of noble metal catalysts is limited by two fundamental disadvantages high cost and low availability. Thus, it is important to construct cathodes with small amounts of the noble metal which are obtained, for example, by dispersed platinum on an appropriate support. 

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